Question #6f0e8

1 Answer
May 14, 2016


One equivalent is usually defined as the amount of substance reacted or produced in a red-ox reaction by the transfer of one mole of electrons.


Combustion of methane with oxygen is a convenient example. First write the balanced reaction:

#CH_4 + 2 O_2 -> CO_2 + 2 H_2O#

The oxidation state of the carbon atom goes from -4 to +4, and each of the 4 oxygen atoms goes from 0 to -2, so 8 electrons are transferred in this reaction. It may help to think about this by rewriting the reaction to correspond to 1 mole of electrons transferred:

#1/8 CH_4 + 1/4 O_2 -> 1/8 CO_2 + 1/4 H_2O#

Now it is easy to see that 1/8 mol of methane reacts per mole of electrons. The molar mass of methane is 16 g, so the mass equivalent of methane is #16g * 1/8=2# g

Similarly, the mass equivalent of #H_2O# produced is
#18g * 1/4 = 4.5 g#